1. Field of the Invention
The present invention relates to a radio-frequency (RF) powder and a method for manufacturing the same and in particular to, an RF powder which is used as a powder and is made to be contained in paper or the like to thereby allow information or the like to be read by a radio-frequency electromagnetic field (radio wave) given from the outside, and a method for manufacturing the same.
2. Description of Related Art
Currently, it is considered that integrated circuit (IC) tags are products indicating the beginning of the ubiquitous age. Labels, Suica cards, FeRAM cards, or the like have been developed previously as RF-ID (micro radio identification). Many people expect that the IC tag market will certainly grow larger in the future. However, the market has not grown enough as expected. The reason is that there are problems such as cost, security, and privacy other than technologies, which must be solved socially.
The cost of the IC tag can be reduced by reducing the size of the IC tag chip. It is because the number of IC tag chips obtained from one wafer can be increased if the size of the IC tag chips is reduced. At present, an IC tag chip of 0.4 millimeters square has been developed. This IC tag chip can read 128-bit memory data in the chip with a microwave of 2.45 GHz (for example, refer to Non-patent Document 1).
According to a conventional manufacturing method, however, there have been problems described below when the micro IC tag chips are manufactured from one wafer.
The conventional method for manufacturing the IC tag chips are described in a section of BACKGROUND ART in, for example, Patent Document 1. According to the manufacturing method, a wafer in which ICs are formed on a front surface is subjected to a back grinding process, and a back surface of the wafer is polished to reduce a thickness of the wafer. After that, the wafer is subjected to a dicing process to separate a large number of IC tag chips with a predetermined shape. In the dicing process, the wafer is cut with a dicing saw to be separated into a large number of IC tag chips. With the separation method for cutting the wafer along dicing lines with the dicing saw, wafer areas, such as considerable areas used for the cutting, areas influenced by the cutting process, and the like, cannot be used for manufacturing the IC tag chips. Furthermore, the smaller the IC tag chips become, the further increases the number of dicing lines, and thus a ratio of unusable area to the whole wafer is increased, thereby making it impossible to use the wafer effectively. Namely, the number of IC tag chips which can be cut out from one wafer is decreased.
For that reason, a new method for separating semiconductor devices is proposed in order so solve the above-described problems in Patent Document 1. According to the method for separating the semiconductor devices in Patent Document 1, half cuts are formed by etching the separating positions for separating the semiconductor devices, from a front surface of the wafer on which circuits are formed; a tape material is adhesively attached on the front surface of the wafer; a back surface of the wafer is then mechanically polished by only a predetermined thickness while leaving a remaining portion so as not to communicate with the half cutting on the front surface; etching or chemical mechanical polishing is performed from the back surface of the wafer; and the wafer is finally separated into individual semiconductor devices. Since the half cut is formed by etching as described above, cut-out portions can be reduced while a width of the half cutting can also be narrowed, and thus allowing the number of the semiconductor devices obtained from one wafer to be increased.
Patent Document 1: Japanese Unexamined Patent Publication (Kokai) No. 2003-179005
Non-patent Document 1: “Micro radio IC tag chip “μ-chip”” by mitsuo Usami in Applied Physics, Vol. 73, No. 9, 2004, p. 1179-p. 1183